What Causes Meningitis? These Infections, Injuries, and Substances May Be to Blame

Several types of bacteria and viruses are common culprits.

Bacteria is a common cause of meningitis—but it's far from the only culprit behind this serious infection, which impacts roughly 2.5 million people around the world each year, according to the World Health Organization.

"Meningitis is basically the swelling of the meninges," says Claire Wright, evidence and policy manager at the UK-based Meningitis Research Foundation, who explains that the meninges are the membranes that wrap around the brain and spinal cord, helping cushion and protect them from injury.

When those membranes become swollen or inflamed from an agent, injury, or infection, it can prompt symptoms that include a severe headache, fever, light sensitivity, nausea and vomiting, joint pain, rash, and a stiff neck that makes it difficult to move your head or touch your chin to your chest.

Often flu-like in the early stages, the symptoms of meningitis can come on suddenly or over the course of a few days and, depending on the cause, progress rapidly—sometimes in a matter of hours, Wright tells Health. That's why the CDC recommends meningitis vaccines for all preteens and teens, and even some kids and adults.

However, vaccines only offer protection from meningitis caused by certain types of bacteria.

According to the CDC, other meningitis causes include:

  • Viruses
  • Parasites
  • Amoeba
  • Cancers
  • Lupus
  • Certain medications
  • Head injuries
  • Brain surgery

Let's take a closer look at what causes meningitis and how these triggers can affect the severity of the infection.

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Bacterial meningitis causes

Bacterial meningitis is caused by bacteria that get into the bloodstream and then travel to the brain and spinal cord. This type of meningitis is considered one the most serious and deadly.

"Bacterial meningitis is a very time-sensitive neurologic emergency," Marie Grill, MD, a specialist in neuroinfectious diseases at the Mayo Clinic, tells Health. "Getting evaluated promptly and getting proper treatment initiated right away is critical."

There are at least 50 types of bacteria that can cause meningitis, according to the Meningitis Research Foundation. The CDC lists the leading causes of bacterial meningitis in the US as:

  • Streptococcus pneumoniae, which causes pneumococcal meningitis
  • Group B Streptococcus, a common cause of meningitis in newborns
  • Neisseria meningitidis, responsible for meningococcal meningitis
  • Haemophilus influenzae, which causes H. influenzae meningitis
  • Listeria monocytogenes, which causes listeria that can lead to meningitis, per the Mayo Clinic
  • Escherichia coli, which is responsible for most cases of E.coli meningitis in babies less than 3 months old, according to the Meningitis Research Foundation

There are a number of ways that bacteria can enter the body and cause bacterial meningitis, including respiratory secretions, person-to-person contact, and contaminated food. Injuries or infections near the brain, like ear infections or dental abscesses, can also cause bacterial meningitis, says Dr. Grill.

Once in the bloodstream, toxins released from the bacteria can weaken the body's capillaries, allowing blood to escape and causing what appears to be a rash under the skin. "When we see the rash, these reddish-purple spots all over the skin, then we're immediately concerned about the possibility of meningococcal meningitis," Dr. Grill explains.

Certain types of bacterial meningitis come with the risk of a complication called septicemia, or blood poisoning, a severe condition that requires emergency care. "Sepsis is where the bacteria are into the bloodstream and they're replicating in the bloodstream and causing damage," says Wright.

Bacterial meningitis can happen to anyone, but the CDC notes that certain people are at higher risk than others, including:

  • Babies
  • Those in group settings, like college campuses
  • Patients who have certain medical conditions (like HIV or cerebrospinal fluid leak)
  • Patients being treated with certain medications and/or surgical procedures
  • Microbiologists who work with bacteria that cause meningitis
  • Travelers to parts of sub-Saharan Africa or Mecca during especially crowded times

Treatment for bacterial meningitis typically includes hospitalization and antibiotics.

Viral meningitis causes

Like the name suggests, viral meningitis is caused by viruses. In the US, non-polio enteroviruses are responsible for most cases of viral meningitis, per the CDC.

"This happens every fall, usually late summer, where this virus comes in and it's, for the most part, normally a respiratory virus. But this one is able to find its way into the brain and cause some brain inflammation," Frank Esper, MD, pediatric infectious disease specialist, Cleveland Clinic Children's Hospital, tells Health.

Because enteroviruses tend to be weak, Dr. Esper says, in most cases, viral meningitis caused by one of these viruses is unlikely to be acute or fatal.

According to the CDC, other viruses that can cause meningitis are:

  • Herpesviruses
  • Epstein-Barr virus
  • Herpes simplex viruses
  • Varicella-zoster virus (the source of chickenpox and shingles)
  • Mumps virus
  • Measles virus
  • Influenza virus
  • Arboviruses (viruses transmitted through certain insects like mosquitoes)
  • Lymphocytic choriomeningitis virus (which comes from rodents, per the CDC)

Regardless of what causes viral meningitis, it's generally considered non-life-threatening, and most people recover without treatment in 10 days or less, according to the CDC. However, in some cases, it can lead to serious illness that requires hospitalization.

Fungal meningitis causes

Fungal meningitis happens when a fungal infection spreads to the brain or spinal cord from another part of the body, according to the CDC.

Cryptococcus neoformans is one the most common causes of fungal meningitis, per the CDC. Harmless to most people, the fungus most often causes cryptococcal meningitis in people with immune deficiencies and conditions like cancer and HIV.

Other fungal meningitis causes include candida albicans (the fungus that can cause thrush and yeast infections) and histoplasma, a fungus found mainly in the soil with large quantities of bird or bat feces. (Inhaling the spores of that fungus can cause a lung infection that can spread to the brain or spinal cord, CDC explains.)

Anyone can get fungal meningitis, but it's relatively uncommon, says Wright, who explains that people with compromised immune systems are typically more susceptible to developing the disease.

According to Dr. Grill, symptoms of fungal meningitis can sometimes be less acute than other types of the disease. "Most people will have headaches that have been going on for weeks even, before that is diagnosed, because it's a chronic infectious process for the most part," she says.

The treatment for fungal meningitis typically involves high doses of antifungal medications administered through an IV, followed by oral versions of those drugs, per the CDC. How long treatment takes depends on a person's overall immune system and which fungus caused the meningitis.

Related: These Are the 6 Main Types of Meningitis, According to Neurologists and Infectious Disease Doctors

Parasitic meningitis causes

There are a number of parasites that can cause meningitis, according to the CDC. These include:

  • Angiostrongylus cantonensis
  • Baylisascaris procyonis
  • Gnathostoma spinigerum

These pathogens typically infect animals—not people. But a person can develop parasitic meningitis if they consume food or animal products contaminated by certain parasites.

Some of these pathogens can cause a rare type of meningitis called eosinophilic meningitis, caused by eating undercooked snails, shellfish, crabs, lizards, and frogs, according to the Encyclopedia of the Neurological Sciences. Consuming raw freshwater fish, eels, poultry, or snakes with these parasites can also cause meningitis.

People at risk for parasitic meningitis are those who live in certain geographic regions of the world, including Southeast Asia, as well as travelers to those destinations. "If you had international travel, depending on where you went, we might think about parasites as potential causes," says Dr. Grill.

There's no specific treatment for eosinophilic meningitis other than managing symptoms, according to the CDC.

Amebic meningitis causes

A type of amoeba called Naegleria fowleri can cause meningitis. This bug can be found in soil and warm freshwater around the globe, often entering the body through the nose when a person is swimming or submerging their heads in religious rituals, according to the CDC. It can also cause amebic meningitis if someone irrigates their nose with contaminated tap water.

Amebic meningitis is often fatal. But it's also extremely rare. The CDC notes that it received 148 reports of infections in the US from 1962 to 2019, with no more than eight known infections every year.

As for treatment, a few medications have shown to be effective against this amoeba in laboratory settings, according to the CDC. How effective they may be in actual patients remains unclear due to the deadliness of amebic meningitis.

Non-infectious meningitis causes

Though uncommon, meningitis can be caused by something other than an infection. "It's an inflammation, but it's not being caused by a germ," says Dr. Esper. "It's being caused by something else, usually a medication, sometimes a tumor or a malignancy of some sort."

According to the Merck Manual, certain vaccines and antibiotics can also cause non-infectious meningitis, as well as over-the-counter medications like NSAIDs (nonsteroidal anti-inflammatory drugs).

Other possible non-infectious meningitis causes include lupus, cancer, head injuries, and brain surgery, per the CDC.

Symptoms of non-infectious meningitis present similar to other types of meningitis and include headache, fever, and stiff neck. However, in some cases, they can be less severe and develop more slowly, according to the Merck Manual.

The treatment for non-infectious meningitis depends on what's causing the inflammation. Often, if the cause of the meningitis is unclear, preventative antibiotics are started until the cerebrospinal fluid is tested and the trigger is determined. If it's a drug or medicine, then the medication is stopped.

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